Partition of respiratory mechanics in patients with acute respiratory distress syndrome and association with outcome: a multicentre clinical study.

PURPOSE: In acute respiratory distress syndrome (ARDS), physiological parameters associated with outcome may help defining targets for mechanical ventilation. This study aimed to address whether transpulmonary pressures (PL), including transpulmonary driving pressure (DPL), elastance-derived plateau PL, and directly-measured end-expiratory PL, are better associated with 60-day outcome than airway driving pressure (DPaw). We also tested the combination of oxygenation and stretch index [PaO2/(FiO2*DPaw)]. METHODS: Prospective, observational, multicentre registry of ARDS patients. Respiratory mechanics were measured early after intubation at 6 kg/ml tidal volume. We compared the predictive power of the parameters for mortality at day-60 through receiver operating characteristic (ROC) and assessed their association with 60-day mortality through unadjusted and adjusted Cox regressions. Finally, each parameter was dichotomized, and Kaplan-Meier survival curves were compared. RESULTS: 385 patients were enrolled 2 [1-4] days from intubation (esophageal pressure and arterial blood gases in 302 and 318 patients). As continuous variables, DPaw, DPL, and oxygenation stretch index were associated with 60-day mortality after adjustment for age and Sequential Organ Failure Assessment, whereas elastance-derived plateau PL was not. DPaw and DPL performed equally in ROC analysis (P = 0.0835). DPaw had the best-fit Cox regression model. When dichotomizing the variables, DPaw ≥ 15, DPL ≥ 12, plateau PL ≥ 24, and oxygenation stretch index < 10 exhibited lower 60-day survival probability. Directly measured end-expiratory PL ≥ 0 was associated with better outcome in obese patients. CONCLUSION: DPL was equivalent predictor of outcome than DPaw. Our study supports the soundness of limiting lung and airway driving pressure and maintaining positive end-expiratory PL in obese patients.

High-Flow Oxygen Therapy Application in Chronic Obstructive Pulmonary Disease Patients With Acute Hypercapnic Respiratory Failure: A Multicenter Study.

OBJECTIVES: To evaluate the effect of high-flow oxygen implementation on the respiratory rate as a first-line ventilation support in chronic obstructive pulmonary disease patients with acute hypercapnic respiratory failure. DESIGN: Multicenter, prospective, analytic observational case series study. SETTING: Five ICUs in Argentina, between August 2018 and September 2019. PATIENTS: Patients greater than or equal to 18 years old with moderate to very severe chronic obstructive pulmonary disease, who had been admitted to the ICU with a diagnosis of hypercapnic acute respiratory failure, were entered in the study. INTERVENTIONS: High-flow oxygen therapy through nasal cannula delivered using high-velocity nasal insufflation. MEASUREMENTS AND MAIN RESULTS: Forty patients were studied, 62.5% severe chronic obstructive pulmonary disease. After the first hour of high-flow nasal cannula implementation, there was a significant decrease of respiratory rate compared with baseline values, with a 27% decline (29 vs 21 breaths/min; p < 0.001). Furthermore, a significant reduction of Paco2 (57 vs 52 mm Hg [7.6 vs 6.9 kPa]; p < 0.001) was observed. The high-flow nasal cannula application failed in 18% patients. In this group, the respiratory rate, pH, and Paco2 showed no significant change during the first hour in these patients. CONCLUSIONS: High-flow oxygen therapy through nasal cannula delivered using high-velocity nasal insufflation was an effective tool for reducing respiratory rate in these chronic obstructive pulmonary disease patients with acute hypercapnic respiratory failure. Early determination and subsequent monitoring of clinical and blood gas parameters may help predict the outcome.

Prevalence of Reverse Triggering in Early ARDS: Results From a Multicenter Observational Study.

BACKGROUND: The prevalence of reverse triggering (RT) in the early phase of ARDS is unknown. RESEARCH QUESTION: During early ARDS, what is the proportion of patients affected by RT, what are its potential predictors, and what is its association with clinical outcomes? STUDY DESIGN AND METHODS: This was prospective, multicenter, and observational study. Patients who met the Berlin definition of ARDS with less than 72 h of mechanical ventilation and had not been paralyzed with neuromuscular blockers were screened. A 30-min recording of respiratory signals was obtained from the patients as soon as they were enrolled, and the number of breaths with RT were counted. RESULTS: One hundred patients were included. ARDS was mild to moderate in 92% of them. The recordings were obtained after a median of 1 day (interquartile range, 1-2 days) of ventilation. Fifty patients had RT, and most of these events (97%) were not associated with breath stacking. Detecting RT was associated with lower tidal volume (Vt) and less opiate infusion. The presence of RT was not associated with time to discontinuation of mechanical ventilation (subdistribution hazard ratio, 1.03; 95% CI, 0.6-1.77), but it possibly was associated with a reduced hospital mortality (hazard ratio, 0.65; 95% CI, 0.57-0.73). INTERPRETATION: Fifty percent of patients receiving assist-control ventilation for mild or moderate ARDS, sedated and nonparalyzed, demonstrate RT without breath stacking on the first day of mechanical ventilation. RT may be associated with low VTS and opiate doses. TRIAL REGISTRY: ClinicalTrials.gov; No.: NCT02732041; URL: www.clinicaltrials.gov.

Automatic detection of reverse-triggering related asynchronies during mechanical ventilation in ARDS patients using flow and pressure signals.

Asynchrony due to reverse-triggering (RT) may appear in ARDS patients. The objective of this study is to validate an algorithm developed to detect these alterations in patient-ventilator interaction. We developed an algorithm that uses flow and airway pressure signals to classify breaths as normal, RT with or without breath stacking (BS) and patient initiated double-triggering (DT). The diagnostic performance of the algorithm was validated using two datasets of breaths, that are classified as stated above. The first dataset classification was based on visual inspection of esophageal pressure (Pes) signal from 699 breaths recorded from 11 ARDS patients. The other classification was obtained by vote of a group of 7 experts (2 physicians and 5 respiratory therapists, who were trained in ICU), who evaluated 1881 breaths gathered from recordings from 99 subjects. Experts used airway pressure and flow signals for breaths classification. The RT with or without BS represented 19% and 37% of breaths in Pes dataset while their frequency in the expert's dataset were 3% and 12%, respectively. The DT was very infrequent in both datasets. Algorithm classification accuracy was 0.92 (95% CI 0.89-0.94, P < 0.001) and 0.96 (95% CI 0.95-0.97, P < 0.001), in comparison with Pes and experts' opinion. Kappa statistics were 0.86 and 0.84, respectively. The algorithm precision, sensitivity and specificity for individual asynchronies were excellent. The algorithm yields an excellent accuracy for detecting clinically relevant asynchronies related to RT.

Efecto de la PEEP sobre el componente resistivo inspiratorio en pacientes con sindrome de distrés respiratorio agudo ventilados a bajo volumen corriente / Effect of PEEP on inspiratory resistance components in patients with acute respiratory distress syndrome ventilated at low tidal volume

RESUMEN Objetivo: Describir el comportamiento del componente resistivo ante el incremento de la presión positiva espiratoria final (PEEP) en pacientes con síndrome de distrés respiratorio agudo ventilados con una estrategia de ventilación protectora. Métodos: En modo controlada por volumen, a 6mL/Kg y flujo constante se realizaron oclusiones teleinspiratorias a PEEP 0, 5 10, 15 y 20cmH2O. Se obtuvieron valores de presión pico, inicial, plateau y se calculó resistencias máxima, mínima y diferencial. Las comparaciones se realizaron mediante test de ANOVA para muestras relacionadas con corrección post hoc de Bonferroni. Se consideró significativo una p < 0,05. Resultados: La resistencia máxima más elevada se observó en los niveles de PEEP más bajos. Los valores de PEEP 10 y 15cmH2O tuvieron diferencias significativas con PEEP 5 y 0cmH2O, mientras que PEEP 20cmH2O únicamente con PEEP 0cmH2O (p < 0,05). La resistencia mínima tuvo la misma conducta que la resistencia máxima. A partir de PEEP 10cmH2O todos tuvieron diferencias significativas con PEEP 0 y 5cmH2O (p < 0,05). La resistencia diferencial se expresó de manera opuesta a la resistencia máxima y mínima. El único nivel de PEEP que experimentó diferencias significativas con PEEP 0 y 5cmH2O fue PEEP 20cmH2O. También hubo diferencias entre PEEP 15 y PEEP 5cmH2O (p < 0,05). Conclusiones: Durante ventilación protectora en pacientes com síndrome de distrés respiratorio agudo, la resistencia máxima del sistema respiratorio tiene un comportamiento decreciente con la PEEP y refleja la respuesta que tiene la resistencia mínima. Mientras que la resistencia diferencial mantiene su conducta creciente con los valores de PEEP.

ABSTRACT Objective: To describe the behavior of inspiratory resistance components when positive end-expiratory pressure (PEEP) increases in patients with acute respiratory distress syndrome under a protective ventilation strategy. Methods: In volume-controlled mode, at 6mL/kg and constant flow, end-inspiratory occlusions were performed at 0, 5 10, 15 and 20cmH2O PEEP. Peak, initial and plateau pressure values were assessed, calculating the maximum, minimum and differential resistances. The results were compared by repeated measures analysis of variance (ANOVA) with post hoc Bonferroni correction, considering p < 0.05 significant. Results: The highest maximum resistance was observed at the lowest PEEP levels. The values for 10 and 15cmH2O PEEP significantly differed from those for 5 and 0cmH2O PEEP, whereas that for 20cmH2O PEEP only significantly differed from that for 0cmH2O PEEP (p < 0.05). The minimum resistance behaved similarly to the maximum resistance; the values for PEEP levels from 10cmH2O to 20cmH2O significantly differed from those for 0 and 5cmH2O PEEP (p < 0.05). Differential resistance showed the opposite variation to the maximum and minimum resistances. The only PEEP level that showed significant differences from 0 and 5cmH2O PEEP was 20cmH2O PEEP. Significant differences were also found between 15 and 5cmH2O PEEP (p < 0.05). Conclusions: During protective ventilation in patients with acute respiratory distress syndrome, the maximum resistance of the respiratory system decreases with PEEP, reflecting the minimum resistance response, whereas differential resistance increases with PEEP.

Effect of PEEP on inspiratory resistance components in patients with acute respiratory distress syndrome ventilated at low tidal volume. / Efecto de la PEEP sobre el componente resistivo inspiratorio en pacientes con sindrome de distrés respiratorio agudo ventilados a bajo volumen corriente.

OBJECTIVE: To describe the behavior of inspiratory resistance components when positive end-expiratory pressure (PEEP) increases in patients with acute respiratory distress syndrome under a protective ventilation strategy. METHODS: In volume-controlled mode, at 6mL/kg and constant flow, end-inspiratory occlusions were performed at 0, 5 10, 15 and 20cmH2O PEEP. Peak, initial and plateau pressure values were assessed, calculating the maximum, minimum and differential resistances. The results were compared by repeated measures analysis of variance (ANOVA) with post hoc Bonferroni correction, considering p < 0.05 significant. RESULTS: The highest maximum resistance was observed at the lowest PEEP levels. The values for 10 and 15cmH2O PEEP significantly differed from those for 5 and 0cmH2O PEEP, whereas that for 20cmH2O PEEP only significantly differed from that for 0cmH2O PEEP (p < 0.05). The minimum resistance behaved similarly to the maximum resistance; the values for PEEP levels from 10cmH2O to 20cmH2O significantly differed from those for 0 and 5cmH2O PEEP (p < 0.05). Differential resistance showed the opposite variation to the maximum and minimum resistances. The only PEEP level that showed significant differences from 0 and 5cmH2O PEEP was 20cmH2O PEEP. Significant differences were also found between 15 and 5cmH2O PEEP (p < 0.05). CONCLUSIONS: During protective ventilation in patients with acute respiratory distress syndrome, the maximum resistance of the respiratory system decreases with PEEP, reflecting the minimum resistance response, whereas differential resistance increases with PEEP.

OBJETIVO: Describir el comportamiento del componente resistivo ante el incremento de la presión positiva espiratoria final (PEEP) en pacientes con síndrome de distrés respiratorio agudo ventilados con una estrategia de ventilación protectora. MÉTODOS: En modo controlada por volumen, a 6mL/Kg y flujo constante se realizaron oclusiones teleinspiratorias a PEEP 0, 5 10, 15 y 20cmH2O. Se obtuvieron valores de presión pico, inicial, plateau y se calculó resistencias máxima, mínima y diferencial. Las comparaciones se realizaron mediante test de ANOVA para muestras relacionadas con corrección post hoc de Bonferroni. Se consideró significativo una p < 0,05. RESULTADOS: La resistencia máxima más elevada se observó en los niveles de PEEP más bajos. Los valores de PEEP 10 y 15cmH2O tuvieron diferencias significativas con PEEP 5 y 0cmH2O, mientras que PEEP 20cmH2O únicamente con PEEP 0cmH2O (p < 0,05). La resistencia mínima tuvo la misma conducta que la resistencia máxima. A partir de PEEP 10cmH2O todos tuvieron diferencias significativas con PEEP 0 y 5cmH2O (p < 0,05). La resistencia diferencial se expresó de manera opuesta a la resistencia máxima y mínima. El único nivel de PEEP que experimentó diferencias significativas con PEEP 0 y 5cmH2O fue PEEP 20cmH2O. También hubo diferencias entre PEEP 15 y PEEP 5cmH2O (p < 0,05). CONCLUSIONES: Durante ventilación protectora en pacientes com síndrome de distrés respiratorio agudo, la resistencia máxima del sistema respiratorio tiene un comportamiento decreciente con la PEEP y refleja la respuesta que tiene la resistencia mínima. Mientras que la resistencia diferencial mantiene su conducta creciente con los valores de PEEP.